Sensors are commonly used to determine whether there is present a predetermined fluid. For instance, sensors are used to determine if hazardous or explosive fluids are present and in what amounts it is present. In such circumstances, it is desired for the sensor and its circuitry to be placed in a protective housing so the dangerous fluid cannot enter and allow propagation of explosion or flame throughout the area.
In order for sensors to be of use their calibration must be correct. If a sensor's calibration is not accurate then it may indicate the presence of a fluid when there is none or the wrong amount of a fluid that could result in an incorrect response by those relying on the readings from the sensor.
For utmost protection and safety it is ideal for a sensor to be calibrated by remote control. There is then no need to remove the protective housing around the sensor and consequently safety is maintained.
There are currently available remote control devices. U.S. Pat. No. 4,156,134 to Minner teaches a remote control device for operation by means of radiation. The devices includes a receiver for the radiation which has means for transforming the radiation into an electric signal and rectification means for rectifying the electronic signal. U.S. Pat. No. 3,289,001 to Wilcox teaches a system for actuating remote electrical circuits with a beam of electromagnetic radiation. U.S. Pat. No. 2,362,832 to Lard teaches a remote control apparatus employing polarized radiation. U.S. Pat. No. 2,903,575 to Palley teaches a remote control system for a wavesignal receiver that is controllable by a light source. U.S. Pat. No. 2,955,777 to Null, et al. discloses an infrared television detector and controller for airborne missiles. However, none of the above teaches a remote control apparatus for calibration of a sensor.
Rexnord gas detection division, Sunnyvale, Calif., does teach two-way communication between a transmitter and calibration meter of a sensor but appears to require a close, exact coupling between components. The calibration indication is outputted to the transmitter. The Rexnord system requires two-way communication therebetween.